Hydroxamic acid catalyzed hydrolysis



United States Patent Ofiice Meme, DQ412222 3,068,072 HYDROXAMIC ACID CATALYZED HYDROLYSIS Mary M. Demek, 1707 Patapsco St., Baltimore 30, Md.; Gerard F. Endres, 12 De Winter Bldg, Netherlands Village, Schenectady, N.Y.; and Joseph Epstein, 4020 Essex Road, Baltimore 7, Md.

No Drawing. Filed Apr. 8, 1960, Ser. No. 21,070 4 Claims. (Cl. 23 230) (Granted under Title 35, US. Code (1952), sec. 266) Riil-NHOH wherein R is any one of numerous hydrocarbon and sub stituted hydrocarbon groups. It has been shown by Hackley et al., 77 Jour. Amer. Chem. Soc. 3651-3653, that hydroxamic acids accelerate the hydrolysis of organic .fluorophosphates and fluorophosphonates, including .the important toxic chemical Warfare agent isopropyl methylphosphonofluoridate, also known as sarin 0r GB. In the course of the reaction the hydroxamic acid is destroyed.

We have found that hydroxamic acids also accelerate the hydrolysisof esters of weak acids, such as acetic acid, In contrast to the hydrolysis of organophosphorus compounds, this latter reaction does not involve the destruc tion of the hydroxamic acid, which acts as a catalyst. In dilute aqueous solutions, the hydrolysis is a first order reaction with respect to the ester. That is, the rate of hydrolysis is proportional 'to the concentration of the ester or:

dc dt where c is the concentratiomt is time and k is the reaction rate constant. We have found, also, that the value of the constant k for a given ester under slightly alkaline conditions is a function of the hydroxamic acid concentration and may be used as a measure of that concentration.

The hydroxamic acids are exceptional as hydrolysis catalysts in that they produce hydrolysis under neutral or only slightly alkaline conditions at room temperature.

One ester that is readily hydrolyzed by use .of the hydroxamic acids is Z-azobenzene-l-naphthyl acetate.

The hydrolysis produces acetic acid and the red dye 2-azobenzene-1-naphthol. The course of the reaction can be followed by measuring the increase in light absorption at a properly selected wavelength. we find that a wavelength of about .54 micron gives optimum results. In practicalapplications we have. employed a Klett-Summerson photoelectric. colorimeter, using a No. 54 filter. The absorption curves of the naphthol and its acetate are given in the article by Epstein, Demek and Wolfi,

Analytical Chemistry, vol. 29, pp; 1050-1053 (July 1957).

The reaction is:

Hio

" it. +orno-on where HA indicates a hydrox-amic acid. I it EXAMPLE 1 The rate of appearance of color .due to Z-azobenzene- 1-napht hol was measured in a solution in which the solyent was a 25% solution of acetone in water bufiered at pH 8.0. The solution was 5 10- M with respect to 'Z-aZobenZene-I naphthyl acetate and hexanehydroxamie acid'and the temperaturewas 25 C. It was established .Ihat the reaction was first order with respect to the acetate, the rate of destruction being5% per minute by .'volume. The rate constant was therefore 5 10- minr EXAM LE 2 The experiments of Example 1 were repeated using a .solvent which was 30% acetone, water. Thereaction rate constant was 2.6X10 'min.'-.

EXAMPLE 3 An extended series of experiments was run. The following solutions were prepared:

' (a) 2-azobenzene-1-naphthyl acetate, 6 -10 M in acetone,

(b) Butter, pH 9.0 (.001 M sodium borate in water).

(0) Hexanehydroxamic acid (HA) in water, various concentrations (see Table 1).

The reaction mixture was formed by mixing these solutions in the following quantities: 5 ,ml. HA solution, 1 ml. butler solution, 4 ml. azobenzenesolution. The mixture was allowed to stand for 5 minutes at 252. C. and the reaction was then stopped by the addition of 0.5 ml. of 0.05 N HCl. The optical density was :then

read .011 the Klet-t-Sum'merson photoelectric colorimeter HA Conc., MXIO un s HAXIO Average EXAMPLE 4 The procedure of Example 3 was repeated employing tion was added, the mixture allowed to stand for five minutes and the reaction stopped by adding 0.5 ml. of the Colorimetric 0.05 N HCl. The optical density was read on the Klett- Summerson photoelectric colorimeter, using the No. 54 filter. The results are shown in Table 3.

In the first column, the sarin (GB) concentration is given on the basis of 6 ml. (four ml. GB solution, one ml. HA solution, one ml. butfer solution). The concentration in the original aqueous solution was 1.5 times that given.

The hydroxamic concentration is likewise given on the basis of the same 6 ml. volume.

The hydroxamic acid remaining (third column) was calculated from the data given in Table 1.

more dilute solutions of hexane hydroxamic acid and al- 10 Table 3 lowlng the mixture to stand for 50 minutes before stopping the reaction by the addition of HCl. GB dd d MX (H Av. ctolorl- Hgirne- H12. t E na r a e 1 meric ma g ace ace The results are shown in Table readings MXIOJ MXHH added Table 2 v n s=|=0.2 3.30 1. 3.00 0.33 1. s9 Av.colorl-' Net colorl- Colorimetric 2. 2.82 0.48 2.27 HA Cone, MXIO- metric metric units 4. 2.32 0.98 2.31 reading Units HAXlO- 2. 00 1. 29 2. 04 MB 1.82 2.15 25 Average 2.13 14 21.2 as a: X.

. 5. 69.0 25.9 E MPLE 6 g The procedure of Example 4 was repeated with the fol- Average 24.6 30 lowing variations. 1

The hexanehydroxamic acid reagent had a concentration It will be noted that the quantity of hydroxamic acid needed to produce the same increase in colorimeter reading is considerably less when the 50 minute reaction period is employed. Compare, for example, 1.32 10' M in Table 1 and 266x10 M in Table 2.

Organophosphorus fluoridates, such as isopropyl methylphosphonofiuoridate, also known as sarin or GB, and diisopropylphosphorofluoridate (DFP) react rapidly with hydroxamic acids in dilute aqueous solution. In the course of the reactions which follow two moles of the acid should be destroyed by each mole of the fluoridate which reacts. Due, however, to a competing reaction producing isocyanates, the consumption of the hydroxamic acid is usually somewhat less than this. See Hackley et al., supra.

We have made the two reactions mentioned above, i.e., the reaction of the fluoridate with a hydroxamic acid and the hydrolysis of 2-azobenzene-1-naphthyl acetate, the basis for an analytical method for sarin. The steps of the method are as follows.

u (1) The fluoridate is allowed to react with a known excess of a hydroxamic acid.

(2) The concentration of the unreacted hydroxamic acid is determined by adding Z-azobenzene-l-naphthyl acetate and measuring the rate of hydrolysis of the acetate as shown by the development of color.

(3) From the concentration of hydroxamic acid before and after the reaction with the fluoridate, the amount of fluoridate is determined.

EXAMPLE 5 The following solutions were prepared:

(a) 2-azobenzene-1-naphthyl acetate, 6X10 M in 100% acetone.

(b) Buffer, pH 9.0 (.001 M sodium borate in water).

(0) Hexanehydroxamic acid (HA) 494x10 M in water.

(d) Sarin (GB) in water, various concentrations (see Table 3).

(e) 0.05 N hydrochloric acid.

In the first step, one ml. of the HA' solution and one m1. of the buffer were added to 4 ml. of the GB solution. The mixture was allowed to stand for 10 minutes at 25 C. Four ml. of the 2-azobenzene-1-naphthyl acetate soluof 5 10 M.

The GB-HA mixture was allowed to stand for one hour at 25 C.

After addition of the 2-azobenzene-1-naphthyl acetate solution, the mixture was allowed to stand for 50 minutes.

The results are shown in Table 4.

Table 4 Av. colori- HA re- HA re- HA re- GB added MXIO' metric maining, acted, acted/GB readings MXIO' M X10 added In the practical use of this method, for the determina tion of concentrations of sarin or similar substances, standardized procedures such as those given in Examples 3 and 4 are carried out and curves are constructed plotting, e.g., GB added against colorimeter reading. The concentration of the unknown can then be determined directly from the colorimeter reading.

We claim:

1. A method of determining the concentration in aqueous solution of hexane hydroxamic acid which comprises adding to said solution 2-azobenzene-1-naphthyl acetate, allowing said solution to stand a fixed length of time and then measuring the optical density of said solution at a wavelength of the order of 0.540 micron.

2. A method for determining the concentration in dilute aqueous solution of a compound selected from the class consisting of phosphonofiuoridates and phosphorofluoridates which comprises adding to said solution an amount of a lower alkyl hydroxamic; acid in excess of that required to react with the amount of said compound believed to be present, allowing said solution to stand for a length of time suflicient for said compound and said acid to react, adding a measured amount of 2-azobenzene-1- naphthyl acetate to said solution, allowing said solution to stand for a fixed length of time, and measuring the optical density of said solution at a wavelength at which 2-azobenzene-l-naphthol has a high light absorption relative to 2-azobenzene-1-n-aphthyl acetate.

3. A method of determining the concentration of the compound isopropyl methylphosphonofluoridate in dilute aqueous solution which comprises adding to said solution a known amount of hexanehydroxamic acid in excess of that required to react with the amount of said compound believed to be present, allowing said solution to stand for a sufiicient length of time for said acid and said compound to react, adding 2-azobenzene-l-naphthyl acetate to said solution and allowing said solution to stand 'for a fixed length of time and measuring the optical density of said solution at a wavelength at which 2-azobenzene-l naphthol has a high light absorption relative to 2-azobenzene-l-naphthyl acetate.

4. A method of determining the concentration of a lower alkyl hydroxa-mic acid in aqueous solution which comprises adding a measured amount of 2azobenzene-1- naphthyl acetate to said solution and determining the rate of hydrolysis by measuring the optical density of said solution at a wavelength at which 2-azobenzene-l-naphthol has a high light absorption relative to that of 2-azobenzene-l-naphthyl acetate.

References Cited in the file of this patent Hackley et aL: Jour. Am. Chem. Soc., vol 77, pages 3651-3653 (1955). v Epstein: Analytical Chemistry, vol. 29, pages 1050- 1953 (1957). 

1. A METHOD OF DETERMINING THE CONCENTRATION IN AQUEOUS SOLUTION OF HEXANE HYDROXAMIC ACID WHICH COMPRISES ADDING TO SAID SOLUTION 2-AZOBENZENE-1-NAPHTHYL ACETATE, ALLOWING SAID SOLUTION TO STAND A FIXED LENGTH OF TIME AND THEN MEASURING THE OPTICAL DENSITY OF SAID SOLUTION AT A WAVELENGTH OF THE ORDER OF 0.540 MICRON. 